- https://falsemachine.blogspot.com/2020/05/soft-ass-d.html (he covers language as a specific part of the post and I think his take is neat)
The RPG Mausritter, about playing as tiny mice in a fantasy world, has some really cool language rules that I don't think can easily work for most other settings:
As a general rule of thumb, the more closely related two creatures are, the more likely they are able to be able to understand each other. Use the creature’s taxonomy to make a ruling. Magical or highly intelligent creatures may break these rules. • Same species (mouse): Can easily communicate. • Same family (rodent): Can speak and communicate, with some difficulty and difference of custom. • Same class (mammal): Make a WIL save to see if communication is possible. • Otherwise: Can’t directly communicate.
So yeah, all those thoughts are very neat. I'll throw in my two cents.